Manufacture of iron



Patented Jan. 11, 1938 v I MANUFACTURE OF IRON Marvin J. Udy, Niagara Falls, N, Y., assignor, by mesne assignments, to Monsanto Chemical Company, a corporation of Delaware No Drawing. Application December 3, 1934, Serial No. 755,767

9 Claims. (Cl. 75-45) This invention relates to the manufacture of ments are present in major proportions, that is, iron, steel and alloys thereof, and has for its in amount, say, above 10% by weight of the alprincipal object the provision of a process for loys. I am not necessarily confined to the use the economic production thereof. of a single alloying element combined with iron A further object of this invention is the proviin the ferrous alloy, but may employ an alloy 5 vion of a process for the production of iron of a containing two or more alloyi Elements high degree of purity, bined with iron. Examples of suitable alloys are A still further object of this invention is the f D SP 0 S 0 ferr0manganBSe-ph0S recovery of phosphatic values in the metallurgy phide, ferromanganese-silicon. Inthe case where of iron. two or more alloying elements combined with 10 In previously known related processes it is the iron are employed, I prefer to have the sum of practice to treat a phosphatic pig iron, to which such alloying elements other than iron total at may have been added scrap iron, with lime and least 10 per cent of the weight of the alloy, aliron ore or mill scale until the impurities have though such requirement is subject to some debeen decreased to the desired degree. In a modifigree of flexibility, as will later more fully appear. cation of the basic open-hearth process, known as In addition to the alloying constituents present the Hoesch process (Bradley StoughtonMetalin major proportion, most ferrous alloys contain lurgy or Iron and Steel-1913, page 149) wherein varying amounts of elements which may be a highly phosphatic slag is recovered, this process termed impurities. These elements may consist 0 results in the production of steel. This process of sulfur, titanium, vanadium, chromium, tin, etc. utilizes a relatively low slag volume and results, Another source of the minor impurities entering during the first part thereof, in the removal of my process will consist in the use of scrap iron, 55% of the carbon, 86% of the phosphorus, 64.6% the application of which will presently more fulof the manganese, and 38% of the sulfur, together ly appear. with all of the silicon. From these results it is A further variation of my process is exemplievident that sulfur is removed with great diflified by the production of pure or ingot iron. As culty and that the removal of the remaining imi ll kn wn in the production of pure iron, it purities, with the exception of silicon, is also ath been customary to use pig iron or scrap with tended With some degree of difficultyas low a content of impurities as possible, and 0 I have now diSCOVeIBd that the manufacture then to treat the molten bath with suitable elimf i n /0r s l m y be n i y simp iinating agents to combine with the impurities .fied and a purer Product Obtained-1f, instead of present. Such treatment was necessarily carselecting a raw material with a low content of ried ut in a high powered openhearth furnace impurities. I deliberately 0110089 P p an and involved a long-time treatment at a high 35 alloy of high. relatively high, impur ty 00 temperature. The production of pure or ingot tent and then remove the impurities n t e iron by these prior processes involved the care- 5 y means of the P p Slagy discovery ful selection of the raw materials; for example, it is based upon the observation that when such alwas customary to select, as a starting material, a

0 loys as ferrophosphorus, ferrosilicon or ferropig mm of the following analysis: manganese, which normally contain a relatively Phosphorus-n0t over 1.00 and as low as poshigh proportion of the alloying constituents, are ible, treated with a basic oxidizing slag, not only are Sulfur-not over 0.05 and as low as possible.

those elements wh are P e in maj r pr0- Silicon-not over 2.00 and as low as possible. portions efiectively removed but the ordinary im- Instead of employing materials of a high depurities which are present in minor proportions, gree of purity, that is a high iron content, I such as sulfur, tin, and others, are also removed make use of ferro-alloys having a comparaand more efiectively than has hitherto been obtively low iron content and treat such alloys in served. the molten state with a basic oxidizing slag 50 For the purpose. of the present specification whereby the major alloying elements, together and claims I shall confine myself-to' ferrous al-, with the impurities present therein, and those loys, such alloys having, in addition to the iron added by the addition agents, are substantially necessarily present, alloying elements such as eliminated. By this means I may obtain a pure 5 phosphorus, silicon and manganese, which eleor ingot iron in which the ordinary impurities may be within the following ranges in percentages:

Phosphorus 0.10 to 0.001 Silicon 0.10 to 0.004 Carbon 0.14 to 0.01

Sulfur 0.003 to 0.001

-were hitherto known. Regarding the content of the major alloying element, it may be said, as a general principle, that I desire'such element to be as high as practical, the actual percentage being usually dictated by economic considerations. This 7 upper limitation is suggested by my observation that the scavenging effect on metalloids or minor impurities which are usually difficult to remove will be a maximum. It is also my observation that the amount of the major alloying element present in the metallic raw material may he graduated to suit the amount of minor non-metallic raw materials to be removed during the refining operation. In general it may be said that the greater the amount of the major alloying element scavenged from the molten alloy, the greater will be the elimination of the associated minor impurities.

As a practical example of my process, I will describe its operation with respect to the treatment of ferrophosphorus, this being an alloy of iron and phosphorus of commercial importance at the presenttime.

For practical purposes I prefer to use, as starting material, a commercial grade of ferrophosphorus, such, for example, as may be prepared by smelting phosphatic and iron-bearingmaterials either in the blast or electric furnace. Such materials usually have a phosphorus content varying from 15% to 28% and, as such, are directly usable in my process. In many cases, however, I may add to such commercial iron-phosphorus alloys an additional amount of iron either as cast iron or scrap, being careful, however, that the total phosphorus content of the mixture is not lowered appreciably below 10% For the purpose of the present specification and claims, I shall designate such an alloy as an iron containing a relatively high proportion of phosphorus, since, as may be seen from the prior art, the phosphorus content is much greater than that hitherto considered prac- I ticable.

Accordingly, I produce first an iron-phosphorus alloy or ferrophosphorus either by smelting scrap iron and phosphatic material in an electric furnace according to the method taught by Garethers in U. S. Patent 1,410,550, or that described by Gray in U. S. Patent 831,427. The source of iron in the former case may be any suitable scrap material or it may be an ore of iron. In the latter process ore is usually employed. The ferrophosphorus produced in the electric furnace will vary in content from 17% to 28% phosphorus, and from 0.1% to 3.0% silicon; while that produced in the blast furnace will average 16% to 21% phosphorus, 0.1% to 1.0% silicon, and, 0.1% to 1.0% sulfur.

I next provide av basic lined furnace, either a gas-fired, open-hearth or an electric type being suitable, and, if conveniently located to the ferrophosphorus furnace, I may charge the basic furnace directly with molten ferrophosphorus. Before charging the furnace with the molten ferrophosphorus, it is desirable to provide a basic oxidizing slag, which is "done by charging to the furnace a mixture of lime and iron ore. The proportions used Will usually approximate 14 pounds of lime to 20 pounds of iron ore'containing, say, 76% F6203, although these proportions may be varied to suit the requirements of the refining operation and of the slag produced. The molten ferrophosphorus is then run into the furnace at a controlled rate so that the reaction does not become too violent.

A rapid elimination of the phosphorus now takes place with considerable evolution of heat in the bath. When the phosphorus in the metal has decreased to from 1 to 3 per cent, the slag is removed and replaced with a fresh slag of the same character as first used. The refining opera tion is continued at a high heat until the phosphorus in the metal has been reduced to between 0.10% and 0.001%. At this point the metal is withdrawn into a ladle, and degasifying or deoxidizing agents are added. These may consist of aluminum or ferrotitanium in relatively small amounts. The molten alloy is now cast into ingot molds.

In certain cases I may employ the ferrophosphorus in lump form, by adding such material directly to the basic oxidizing slag. By proper choice of lump size the vigor of the reaction may be controlled. During the addition of the ferrophosphorus lumps or before such addition, I may add additional quantities of iron as cast or scrap iron.

Because of the rapidity with which the charge. can be heated in the electric furnace, some advantage will result from operating in this type of furnace. There will be a greater contamination with carbon when operating in such a furnace; however, for'certain purposes this may not be objectionable.

The amount of basic oxidizing slagused in the first refining is proportioned so that it will contain from 18 to 24% of phosphoric acid as P205 when finished, although this figure will vary, somewhat.

In prior processes for the production of steel and iron the amount of slag formed amounted to from 10% to 30% by weight of the amount of such iron or steel treated. My process, on the other hand, consists in the treatment of iron alloys with from to 400% by weight of slag based on the amount of iron produced.

An examination of the metal from under the first slag produced as described above shows that the metalloids, other than phosphorus, have been substantially removed from the iron.

The amount of basic oxidizing slag used in the second refining operation may be equal in amount to that first used; Because of the lower phosphorus in the metal, however, such slag will contain less phosphoric acid. The removal of the refined metal from below this second slag is conveniently done by pouring it from below, as is done in a tilting furnace. The second slag will then remain in the furnace and, being of low phosphorus content, may be used as a first refining slag in a subsequent operation. Additional quantities of slagging ingredients may be added, if desired.

The impurities present in the iron produced J according to my process will be within the following ranges:

Phosphorus. 0.10 to 0.001 Silicon 0.10 to 0.004 Carbon 0.14 to 0.01 Sulfur- 0.003 to 0.001

The actual amount of impurity present in the iron produced by my process will be dependent upon the type of furnace used and the care taken in operating the same. In general, a slightly higher carbon content will be obtained in the electric furnace than in the open-hearth furnace.

The pure iron produced will analyze between 99.56 and 99.98% Fe, and is especially suited for uses where a high degree of corrosion resistance is desired. Because of its freedom from the usual impurities, it is also favored for the manufacture of special iron alloys or steel. 1

The intermediate product produced under the first refining slag may contain from 0.6 up to 2 or 3 per cent of phosphorus. If the phosphorus is to be further reduced by a subsequent treatment, it is advantageous to stop the treatment with the first slag when the phosphorus in the metal is in the neighborhood of 2 or 3 per cent.

If, however, a high phosphorus ingot iron is desired, it is best to carry the scavenging of the phosphorus down with the first slag until the content of this element is in the range of from 0.65 to about 1.07% phosphorus. When carried to this point, the minor impurities present, namely, the carbon, manganese, silicon and sulfur, will total in the aggregate less than 0.30% and usually somewhat more than 0.015% of the alloy.

The high phosphorus iron may be cast into ingots, forged and rolled or otherwise fabricated. When hot rolled and annealed, a 22-gauge iron sheet prepared from an ingot iron containing between 0.65% and 1.07% phosphorus will have an ultimate tensile strength of from 80,000 to 85,500 pounds per square inch, 2. yield point of 70,000 to 13,000 pounds per square inch, and an elongation in 2 inches of from 15% to 20%.

While I am uncertain as to the exact reason for the almost complete elimination of the impurities in the metal produced by my process, I believe it to be connected with the elimination of the large amount of the major alloying element such, for example, as phosphorus present in proportion to the iron. Apparently the scavenging of the large quantities of phosphorus which I employ carries into the slag most of the impurities present in the iron and iron ore.

This scavenging action is particularly noticeable in the case of sulfur, which may be present in the original raw materials in rather large quantities. I have found, for example, in one case that where sulfur was present in the ferrophosphorus alloy to the extent of 0.65%, one treatment with a basic oxidizing slag served to reduce the amount of this impurity to 0.03%. This corresponds to a sulfur elimination of 96%.

The scavenging action of the phosphorus present in the high phosphorus-iron alloy is, of course, not confined to its effect on sulfur, but is also effective in removing silicon, manganese, tin, etc. As I have indicated above, the metal resulting from my process is characterized by a very low content of those impurities normally present in commercial iron or steels, and is thereby distinguished over the prior art products and process.

My process is effective, as has already been stated, not only with ferrophosphorus but also with ferrosilicon, ferromanganese and mixtures of these alloys. For most practical results I prefer to limit the content of the major alloying elements to between on the lower side to as high as 28% on the upper side, the remaining element being essentially iron. When working within these limits, which, as has already been stated, may be varied depending upon conditions, I have found that removal of the minor impurities occurring in ferro alloys becomes a comparatively simple process.

Having obtained a purified iron by the abovedescribed process, I may produce therefrom either carbon steel or any of the various alloy steels by the addition of'the proper alloying constituents.

In the foregoing specification I have described various specific means by which my process may be carried out. It will be apparent, however, to those skilled in the art that my invention is susceptible to various changes and modifications without departing from the spirit thereof; and I desire, therefore, that my invention be not limited to any specific modifications except as indicated by the prior art or as specifically set out in the appended claims.

What I claim is:

1. The process of eliminating impurities from molten iron alloys, and producing a substantially pure ingot iron comprising scavenging therefrom by oxidation a relatively large proportion of phosphorus, such proportion of phosphorus removed comprising more than 10% by weight of the alloy. 1

2. The process of producing an ingot iron containing upwards of 99.56% Fe, comprising first forming an iron-phosphorus alloy containing at least 10% of phosphorus and then scavenging said alloy by oxidation to remove therefrom said phosphorus.

3. The process of producing iron containing upwards of 99.56% Fe, comprising first forming an iron-phosphorus alloy having at least 10% of a relatively high phosphorus content and. then refining said alloy by oxidation with a basic slag to remove said phosphorus.

i. The process of producing iron of relatively high purity, comprising first forming an ironphosphorus alloy with more than 10 per cent of phosphorus and then refining said alloy with a basic oxidizing slag to remove substantially all of said phosphorus.

5. The process of producing ingot iron of relatively high purity, comprising first forming an iron-phosphorus alloy having a phosphorus content within the range of from 10 to 28 per cent and then refining said alloy with a basic oxidizing slag to remove substantially all of said phosphorus.

6. The process of producing pure ingot iron from iron containing the usual impurities, comprising first forming a high-phosphorus iron alloy containing between and 28 per cent of phosphorus together with impurities and thereupon refining said alloy with a basic slag under oxidizing conditions to remove substantially all of said phosphorus together with said impurities.

'7. In the process of producing pure ingot iron from iron containing impurities, the step of refining an iron alloy having at least 10% of phosphorus content with a basic slag under oxidizing conditions to remove substantially all of said phosphorus.

8. In the process of producing pure ingot iron from iron alloys containing impurities, the steps 75 3- aioaoao of refining an iron alloy containing between 15 and 28 per cent of phosphorus together with a minor amount of sulfur with a basic slag under I oxidizing conditions to remove substantially all of said phosphorus and sulfur.

9. The process of eliminating impurities from molten iron alloys, and producing a substantially pure ingot iron, comprising scavenging therefrom by oxidation a relatively large proportion of the elements phosphorus, silicon and manganese, the proportion of said elements removed comprising in the aggregate more than 10% by weight of 5 the said alloy.

MARVIN J. UDY. 

